There are three types of cutting heads for vegetation trimmers that use filaments for cutting the vegetation: manual, semiautomatic, and automatic. With manual and semiautomatic vegetation trimmers, the operator must monitor filament wear. When the filament becomes too short to be effective, the filament must be extended or replaced by the operator. Today most filament vegetation trimmers come equipped with manual or semiautomatic cutting heads.
An operator using a manual vegetation trimmer is responsible for monitoring the filament length and adjusting its length as needed to maintain effective cutting. The operator must stop the trimmer to a) manually extend the filament; or b) discard the stub length of old filament, install a new length of filament and manually extend the filament to the correct starting length. Using manual vegetation trimmers also means taking valuable time to adjust the filament to the correct cutting length.
If the operator is using a semiautomatic vegetation trimmer, the operator is also responsible for monitoring the filament length and adjusting the filament length to maintain the appropriate cutting length. When the operator detects that the filament needs adjustment, the operator must take the time to directly activate a mechanism to extend the filament. For these semiautomatic systems it is not always necessary to stop the trimmer before making a filament length adjustment. If the filament needs replacement then the trimmer must be stopped before replacing the filament on the spool. Using semiautomatic vegetation trimmers also means interrupting the trimming operation and taking valuable time to adjust the filament to the correct cutting length. Some filament is wasted when only a portion of the length needs replacement and an excess of what is needed is automatically released. In addition, because semi-automation means a greater number of active parts, the initial purchase price for the device is higher as is the likelihood of having to repair or replace parts for proper operation.
With an automatic vegetation trimmer, the operator does not need to monitor the filament length. Without operator intervention, an automatic vegetation trimmer cutting head periodically extends a new fixed length of filament. Filament is deployed from an internal spool through a hole in a housing upon an automatic mechanism's periodic (a) release of a spool brake or (b) indexing of the spool by advancing it to its next predefined position.
In some automated trimmers, a counterweight counterbalances the filament tension and the automatic mechanism is activated by the mechanism's detection of reduced filament tension. During operation, other automatic vegetation trimmers activate the automatic mechanism upon detecting the filament spool's increased rotational speed beyond some preset range.
Cutting swath size fluctuations are inherent in automatic and semiautomatic vegetation trimmers whose automatic feeding mechanisms deliver a fixed length of filament with each activation. Some filament is wasted when only a portion of the length needs replacement and the automated mechanism releases an excess of what is actually needed. If the extended filament is too long, the trimmer is overloaded and its motor may fail prematurely. Electric trimmers are especially sensitive to overloading. Motor overloading due to the stress of overlong extended filaments is a problem common to manual, semiautomatic, and automatic vegetation trimmers.
Ideally, to conserve filament, only the tip of the extended filament should strike the vegetation. While the automatic or semiautomatic vegetation trimmer is engaged in trimming vegetation, each time the size of the cutting swath suddenly increases by some fixed automatically dispensed length of filament, a segment at the distal end of the extended filament impacts the vegetation. While operating with an increased cutting swath, more than the tip of the extended filament strikes the vegetation. The extended filament segment making contact with the vegetation receives impact damage throughout its length. This impact damage results in premature filament failure and the periodic loss of whole segments of filament.
An overly long filament segment is likely to fail at a point recessed back from the tip. The result is the periodic loss of whole segments of filament rather than the gradual wear of material from the tip. To prevent excessive length, some prior trimmers are equipped with a cutoff blade positioned to cut off excess filament. Not only does this waste filament, but the severed flying tip is annoying or even dangerous.
Significant wear accumulates before the activation threshold of the automatic filament feeding mechanism is exceeded. Automatic and semiautomatic vegetation trimmers operate in a cycle of gradual declines and sudden increases in the cutting swath. This cycle results in wasted filament and difficulty in maintaining refined control of the cutting swath which may result in wasteful repetitive operator motion or inadvertent cuttings.
Automation and semi-automation mechanisms typically found in vegetation trimmers mean a greater number of active parts and corresponding greater complexity and weight. Easily maneuvered weight is important to users that frequently operate the device for long periods as well as infrequent users who may lack physical conditioning to wield the heavier trimmers for even short periods such as would be required in dressing a relatively small vegetation area. The initial purchase price for automatic and semiautomatic devices with their greater number of parts and complexity is higher as is the likelihood of having to repair or replace parts for proper operation. Most automatic and semi-automatic cutting heads must be disassembled for reloading. The casual occasional users and inexperienced users must consult a manual or waste time on trial and error efforts. Reloading seems to be particularly complex.
An ideal vegetation trimmer would (a) minimize wasting the operator's time in non-trimming operation, (b) conserve filament, (c) maintain a consistent and predictable cutting perimeter, (d) have a simplified design to reduce initial purchase cost and maintenance cost, (e) be lightweight, and (f) be simple to operate and reload. The above inventions fail to meet these individual and combined goals for an ideal vegetation trimmer. For the foregoing reasons, there is a need for a fully automatic vegetation trimmer which does not waste filament and which is simple, easy to use, consistent, reliable, and inexpensive.